1. Field of the Invention
This invention relates to a cutting device, in particular to tissue cutting dies for cutting tissues to a particular configuration, especially for the fabrication of tissue leaflets for preparation of an autologous heart valve.
2. Description of the Related Art
Several types of heart valves are presently available for use in replacing diseased or malfunctioning heart valves in humans.
One form of heart valve is constructed from animal tissue, typically from bovine or porcine aortic valve tissue. The valves constructed from animal tissue typically have short lifetimes. The short lifetimes are caused by two factors. First, there is an antigenic reaction by the body to the animal tissue which causes the tissue to calcify, making it inflexible and more susceptible to failure with time. Second, the tissue is often stored in glutaraldehyde before implantation to try to decrease the antigenic reaction. The aldehyde tends to tan the tissue to a leather-like consistency, which makes the tissue wear out from the repeated stress of opening and closing.
Thus, although heart valves containing animal tissue are widely used, most have to be replaced after about five to ten years. Replacing these valves poses risks to the patient, because a second open heart operation is required, with the attendant possibility of problems during the operation.
Mechanical heart valves are also available. The mechanical valves are made of hard, non-biological materials such as metals or ceramics. Although the mechanical heart valves are durable, the hard, non-biological surfaces on the valves tend to cause blood clots. The blood clots can cause heart attacks or strokes, and, as a result, patients with mechanical heart valves must take anticoagulant drugs. These drugs can lead to hemorrhagic complications.
Another type of heart valve, the autologous tissue valve, is constructed with the patient""s own tissue, minimizing the chances of the patient""s body rejecting the implanted tissue. A number of patents for autologous tissue heart valves and methods of making autologous tissue heart valves have issued to Autogenics, assignee of this application, including U.S. Pat. Nos. 5,163,955, 5,326,371, and pending U.S. application Ser. No. 09/161,809.
If the patient""s own tissue is used to construct the heart valve, the valve must usually be assembled in the same surgical procedure in which the patient""s damaged or diseased valve is removed. The valve assembly must be completed quickly to minimize the risk to the patient.
When constructing an autologous heart valve, the patient""s tissue is typically mounted on a stent or other type of frame. In one conventional method, valve leaflets are cut from a piece of tissue and are sewn or attached to the frame. In another method, a single piece of tissue is attached to the frame, and the excess tissue is removed. Both methods are time-consuming, causing risk to the patient. In order to reduce the time required to shape the tissue into a form which can be attached to the frame more quickly, tissue cutting dies have been designed.
Two forms of tissue cutting dies are described in the ""955 patent. In both forms of the dies, the tissue is cut into the desired shape by pressing a die with embedded blades against a piece of tissue, cutting the tissue in a manner similar to a cookie cutter. Another tissue cutting die is described in U.S. Pat. No. 5,425,741. An actuator with a raised ridge is drawn through a slot in the die. The raised ridge forces the tissue against the blade. A tissue cutting die with a rotatable cutting pad was described in U.S. Pat. No. 5,609,600.
The present invention provides an improved apparatus and method for cutting a piece of tissue into tissue leaflets for use in autologous tissue heart valves. A significant factor of the invention is that the tissue cutting die is a rotary tissue cutting die that requires less force to operate than previous tissue cutting dies.
The rotary tissue die includes a flexible backing pad for holding the tissue, a housing containing a plurality of blades with a sharpened edge, and a rotary table with a raised cutting bar on the top surface. The cutting bar forces the flexible backing pad against the sharpened edge of the plurality of blades in the housing when the rotary table is rotated, so that the tissue between the flexible backing pad and the housing is automatically cut through.
The flexible backing pad, the housing containing a plurality of blades, and the rotary table are contained in a generally cylindrical body with an end cap. A shaft on the rotary table is connected to a handle. The flexible backing pad is preferably made of polytetrafluoroethylene. Advantageously, the rotary table is made of stainless steel, and the housing containing the plurality of blades is made of polycarbonate.
The blades, the blade housing, and the backing pad are disposable. The cylindrical body and the end cap can be sterilized and reused.
The tissue cutting die of the present invention is used in the following manner. First, a roughly sized piece of tissue is placed on the surface of the flexible backing pad. The plurality of blades with a razor sharpened edge housed in the housing are placed into contact with the tissue. The end cap and the cylindrical body are aligned and secured together. When the handle is turned to rotate the rotary table, the raised cutting bar forces the flexible backing pad against the razor sharpened edge of the plurality of blades in the housing, so that the tissue between the flexible backing pad and the housing is automatically cut through.